Bearing unit, and motor using same

ABSTRACT

A bearing unit is provided which includes a shaft ( 51 ) to support rotatably, radial bearing ( 55 ) to support the shaft ( 51 ) circumferentially, a thrust bearing ( 66 ) to support the shaft ( 51 ) in the direction of thrusting, and a housing ( 56 ) having the radial bearing ( 55 ) and thrust bearing ( 66 ) disposed therein and in which a viscous fluid ( 57 ) is filled. The housing ( 56 ) has a sealed structure except for a shaft insertion hole ( 65 ) formed therein and through which the shaft  51  is introduced. Between the outer surface of the shaft ( 51 ) and the inner surface of the shaft insertion hole ( 65 ), there is defined a gap ( 69 ) having a sufficient width to prevent the viscous fluid ( 57 ) filled in the housing ( 56 ) from leaking out of the latter. The housing ( 56 ) is formed as a one-piece structure by molding a synthetic resin.

This is a continuation of application Ser. No. 10/416,838, filed on May15, 2003, now U.S. Pat. No. 7,011,449, which is a 371 application ofPCT/JP02/09360 filed on Sep. 12, 2002, the entire contents beingincorporated by reference.

TECHNICAL FIELD

The present invention relates to a bearing unit for supporting arotating shaft rotatably or for supporting a rotating body rotatably ona shaft and a motor using the bearing unit.

BACKGROUND ART

There are already known various types of bearing units for supporting arotating shaft to be rotatable, including a typical one constructed asshown in FIG. 1.

In FIG. 1, the bearing unit is generally indicated with a reference1020. As shown, the bearing unit 1020 is to support a rotating shaft1023 to be rotatable. It includes a metallic housing 1022 shaped as acylinder open at opposite ends thereof and a radial bearing 1021 thatsupports the rotating shaft 1023 rotatably in the housing 1022. Thehousing 1022 has installed in one of the open ends thereof a thrustbearing 1024 that supports, thereon in the direction of thrusting, therotating shaft 1023 supported rotatably in the radial bearing 1021.

The bearing unit 1020 uses a dynamic-pressure fluid bearing as theradial bearing 1021. The dynamic-pressure fluid bearing has formed inthe inner circumference thereof opposite to the rotating shaft 1023 inthe radial bearing 1021 dynamic pressure producing recesses intended toproduce a dynamic pressure.

The housing 1022 is filled with a lubricant that is a viscous fluid andthat is circulated through the dynamic pressure producing recesses whenthe rotating shaft 1023 rotates to produce a dynamic pressure.

The rotating shaft 1023 is inserted in the radial bearing 1021 andreceived rotatably in the housing 1022, with one end thereof beingsupported on the thrust bearing 1024.

The housing 1022 has fixed in the other open end thereof a metallic oilseal 1025 formed to have a toroidal shape, and which prevents thelubricant filled in the housing 1022 from leaking out from inside thelatter. The rotating shaft 1023 is projected out of the housing 1022through a shaft insertion hole 1026 formed in the center of the oil seal1025 and through which the rotating shaft 1023 has been introduced.

To prevent the lubricant filled in the housing 1022 from leaking tooutside, an adhesive is used between the oil seal 1025 and housing 1022to provide a complete sealing at a junction 1027 there. The oil seal1025 has applied to the inner surface thereof a surfactant to preventthe lubricant from being moved out of the housing 1022 through the shaftinsertion hole 1026 under a centrifugal force developed by the rotationof the rotating shaft 1023.

In the bearing unit 1020 constructed as shown in FIG. 1, the lubricantfilled in the housing 1022 will flow through only a gap 1031 definedbetween the outer surface of the rotating shaft 1023 and the innersurface of the shaft insertion hole 1026 (inner surface of the toroidaloil seal 1025). It should be noted that with the gap 1031 reduced inwidth, the lubricant will have the surface tension thereof increasedcorrespondingly and thus can prevent itself from leaking out of thehousing 1022.

Further, the rotating shaft 1023 is tapered (indicated at a reference1030) at the outer surface thereof opposite to the inner surface of theshaft insertion hole 1026. Namely, the rotating shaft 1023 is taperedoutwardly of the housing 1022. The taper surface 1031 will yield apressure gradient in the gap 1031 defined between the taper surface 1030itself and the inner surface of the shaft insertion hole 1026, so that acentrifugal force developed when the rotating shaft 1023 rotates willcause a force with which the lubricant filled in the housing 1022 ismoved inwardly of the latter. Since the lubricant is thus moved inwardlyof the housing 1022 when the rotating shaft 1023 rotates, it willpositively enter the dynamic pressure producing recesses in the radialbearing 1021 formed from a dynamic-pressure fluid bearing to produce adynamic pressure that will assure a stable supporting of the rotatingshaft 1023 and prevent the lubricant filled in the housing 1022 fromleaking out.

As above, the aforementioned bearing unit 1020 is constructed of thehousing 1022, the thrust bearing 1024 and the oil seal 1025, each beingan independent member. The number of parts of this bearing unit 1020cannot be said to be small. In addition, the sealant, such as anadhesive, has to be used to form the oil-tight junction 1027 between thehousing 1022 and oil seal 1025, which will cause the assembling of thebearing unit 1020 to be complicated.

Further, use of an adhesive as a sealant will hardly attain any completesealing at the junction 1027 between the housing 1022 and the oil seal1025 and permit no positive prevention of the lubricant filled in thehousing 1022 from leaking out. To prevent the lubricant from leaking, asurfactant has to be applied to the surface of the oil seal 1025, whichalso will make the production of a bearing unit of this type morecomplicated.

As mentioned above, the conventional bearing unit includes many partsand thus is difficult to assemble. No positive sealing of the lubricantis possible. Therefore, conventional bearing units are expensive.

Also, a motor using a bearing unit of the above-mentioned type will bean assembly of many parts, thus difficult to assemble, and so it is notproducible with less costs.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention has an object to overcome theabove-mentioned drawbacks of the related art by providing a novelbearing unit and a motor using the bearing unit.

The present invention has another object to provide a bearing unit witha smaller number of parts, easier to assemble and more reliable and amotor using the bearing unit.

The present invention has still another object to provide a bearing unitin which a viscous fluid, such as a lubricant or the like, filled in ahousing can be prevented from leaking out and a motor using the bearingunit.

The present invention has yet another object to provide a bearing unitin which a viscous fluid filled in a housing can be prevented from beingcaused to leak out by an environmental change, such as abarometric-pressure change.

The present invention has still yet another object to provide a bearingunit installable easily and positively in a predetermined position, suchas a stator of a motor or the like.

The present invention also has another object to provide a bearing unitin which static electricity developed at a rotating portion, such as ashaft or the like, can be discharged surely to outside to protectpositively an electronic device using the bearing unit and a motor usingthe bearing unit.

The above object can be attained by providing a bearing unit including,according to the present invention, a shaft, a radial bearing to supportthe shaft circumferentially, a thrust bearing to support the shaft atone of the thrusting-directional ends thereof, and a housing in whichthe radial and thrust bearings supporting the shaft are disposed and aviscous fluid is filled, the housing having a hermetic structure exceptfor a shaft insertion hole receiving the shaft therein and in whichthere is a gap, defined between the outer surface of the shaft and theinner surface of the shaft insertion hole, having a sufficient width toprevent the viscous fluid filled in the housing from leaking to outside.

Note that the housing is formed as a one-piece structure by molding asynthetic resin.

Either the inner surface of shaft insertion hole or shaft outer surfaceopposite to the inner surface of the shaft insertion hole is tapered toincrease the gap defined between the shaft outer surface and the innersurface of the shaft insertion hole toward outside the housing.

The viscous fluid filled in the housing is filled up to at least aposition where it is exposed in the gap defined between the shaft outersurface and the inner surface of the shaft insertion hole.

When the shaft or housing is rotated, the taper surface formed on theshaft outer surface or the inner surface of the shaft insertion holewill produce a force that causes the lubricant having entered the gapdefined between the shaft outer surface and the inner surface of theshaft insertion hole to move inwardly of the housing.

The radial bearing is made of a sintered metal and will have impregnatedtherein the viscous fluid filled in the housing.

The radial bearing is a dynamic-pressure fluid bearing and has formed inthe inner surface thereof opposite to the shaft outer surface dynamicpressure producing recesses that produce a dynamic pressure by theviscous fluid.

The thrust bearing supporting the shaft at one end of the latter isformed integrally inside the housing.

The end portion of the housing where the thrust bearing is disposed maybe formed from a synthetic resin and joined by welding to the housingbody also formed from the synthetic resin and in which the radialbearing is disposed.

The thrust bearing is formed integrally at the end portion of thehousing that is welded to the housing body. The thrust bearing may beformed from a metal and integrally at the end portion of the housingthat is welded to the housing body.

The end portion of the housing where the thrust bearing is disposed maybe formed by out-sert molding integrally on the housing body in whichthe radial bearing is disposed.

There may be provided inside the housing a come-off preventive portionto prevent the shaft from coming off in the direction of thrustingthrough the shaft insertion hole.

The thrust bearing used in the bearing unit according to the presentinvention supports a projecting portion formed at one end of the shaftand larger in diameter that the shaft body, and has formed in thesurface thereof opposite to the projecting portion of the shaft dynamicpressure producing recesses to produce a dynamic pressure by the viscousfluid.

The housing of the bearing unit according to the present invention has aprojection provided for mechanically fixing the housing to a matingobject.

The fixing means may be an engagement portion formed on the housingitself, a projection or screw.

The above fixing means assures an accurate positioning of the bearingunit in relation to a mating object for installation of the bearing unitto the latter.

The housing may have provided thereon a metallic member for installationof the housing to a mating object by bonding.

The housing may have provided thereon a detent to limit the rotation ofthe housing and mechanically fix the housing to a mating object.

Since the shaft, viscous fluid, radial bearing and housing in thebearing unit according to the present invention form together adischarge path leading to outside of the housing, static electricitydeveloped due to the rotation of the shaft or of the housing in relationto the shaft can be discharged to outside the housing.

Further, the bearing unit according to the present invention may haveformed in the housing a communication path that provides a communicationof the inside of the housing where the thrust bearing supports the shaftat one end of the latter with outside of the housing. Because of such acommunication path, air caused to stay inside the housing by anenvironmental change, such as a change in barometric pressure,temperature, etc., can be let to escape to outside the housing, so thatit is possible to prevent the viscous fluid from leaking out of thehousing.

Also, according to the present invention, the above object can beattained by providing a motor including a bearing unit supporting arotor of the motor rotatably in relation to a stator of the motor, thebearing unit being one described above.

In the above motor, the rotor is fixed to the shaft of the bearing unitand thus rotated together with the shaft.

Also, the rotor may be constituted to be supported by the housing androtate together along with the housing.

These objects and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription of the best mode for carrying out the present invention whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a conventional bearing unit.

FIG. 2 is a perspective view of an example electronic apparatusincluding a motor using the bearing unit according to the presentinvention.

FIG. 3 is a sectional view, taken along a line III—III, of theelectronic apparatus shown in FIG. 2.

FIG. 4 is a perspective view of a radiator using the motor according tothe present invention.

FIG. 5 is a sectional view of the radiator provided with the motor usingthe bearing unit according to the present invention.

FIG. 6 is a sectional view of a first embodiment of the bearing unitaccording to the present invention.

FIG. 7 is a perspective view of a radial bearing in the bearing unit inFIG. 6 showing dynamic pressure producing recesses formed in the innersurface of the radial bearing.

FIG. 8 is a sectional view of a gap formed by the outer surface of therotating shaft and the inner surface of the shaft insertion hole in ahousing.

FIG. 9 explains the capillary phenomenon of a fluid.

FIG. 10 is a cross-sectional view of a lubricant having entered the gapdefined between the outer surface of the rotating shaft and the innersurface of the shaft insertion hole.

FIG. 11 is an axial-sectional view of the gap defined between the outersurface of the rotating shaft and the inner surface of the shaftinsertion hole, explaining the difference in suction pressure atportions, having different diameters, of a tapered portion of a rotatingshaft.

FIG. 12 is an axial-sectional view of the gap defined between the outersurface of the rotating shaft and the inner surface of the shaftinsertion hole, showing the lubricant having entered the gap and havingair mixed in the lubricant.

FIG. 13 is a cross-sectional view of the gap defined between the outersurface of the rotating shaft and the inner surface of the shaftinsertion hole, showing that the lubricant in the gap is cut.

FIG. 14 is an axial-sectional view of the rotating shaft positioned inan off-center relation with the shaft insertion hole in the housing.

FIG. 15 is a sectional view of the gap defined between the outer surfaceof the rotating shaft and the inner surface of the shaft insertion hole,showing the lubricant in the gap when the rotating shaft is eccentricwith respect to the shaft insertion hole in the housing.

FIG. 16 is a sectional view of a variant of the first embodiment of thebearing unit according to the present invention, showing that the shaftinsertion hole in the housing has a tapered portion.

FIG. 17 is an axial-sectional view of a second embodiment of the bearingunit according to the present invention.

FIG. 18 is an axial-sectional view of a variant of the second embodimentof the bearing unit shown in FIG. 17.

FIG. 19 is an axial-sectional view of a third embodiment of the bearingunit according to the present invention.

FIG. 20 is an axial-sectional view of a fourth embodiment of the bearingunit according to the present invention.

FIG. 21 is a plan view of a disc drive unit as an example of aninformation recorder/player, including the motor using the bearing unitaccording to the present invention.

FIG. 22 is an exploded perspective view of the disc drive unit in FIG.21, showing its internal mechanism.

FIG. 23 is a further exploded perspective view of the disc drive unit inFIG. 21.

FIG. 24 is a sectional view of a spindle motor according to the presentinvention, having the bearing unit positioned and installed to a statorthereof.

FIG. 25 is a perspective view of the bearing unit having an engagementportion formed thereon to help positioning and installing the bearingunit to the stator of the spindle motor in FIG. 24.

FIG. 26 is a sectional view of a variant of the spindle motor to whichthe bearing unit is positioned and installed.

FIG. 27 is a perspective view of the bearing unit having a positioningprojection provided on the bottom of the housing.

FIG. 28 is a perspective view of another variant of the bearing unitaccording to the present invention, having positioning projectionsprovided on the bottom of the housing.

FIG. 29 is a sectional view of another variant of the spindle motoraccording to the present invention, to which the bearing unit ispositioned and installed.

FIG. 30 is a perspective view of the bearing unit having an externallythreaded projection provided on the bottom of the housing.

FIG. 31 is a perspective view of the bearing unit including a housinghaving an externally threaded portion on the outer surface thereof nearthe bottom.

FIG. 32 is a sectional view of still another variant of the spindlemotor according to the present invention, having the bearing unit fixedby bonding in a cylindrical portion of a stator housing thereof.

FIG. 33 is a perspective view of the bearing unit having a detentprovided on the housing.

FIG. 34 is a perspective view of another variant of the bearing unithaving detents provided on the housing.

FIG. 35 is a perspective view of still another variant of the bearingunit having detents provided on the housing.

FIG. 36 is a perspective view of yet another variant of the bearing unithaving detents provided on the housing.

FIG. 37 is a sectional view of yet another variant of the spindle motoraccording to the present invention, having the bearing unit positionedand installed to a stator housing thereof.

FIG. 38 is a sectional view of a spindle motor according to the presentinvention, in which the housing of the bearing unit is used as a part ofthe stator.

FIG. 39 is a sectional view of a spindle motor according to the presentinvention, whose stator housing is used to form the housing of thebearing unit.

FIG. 40 is a perspective view of a variant of the bearing unit in whichthe housing of the bearing unit is formed from a synthetic resinintegrally with the stator housing of the spindle motor.

FIG. 41 is a perspective view of a variant of the bearing unit, in whichthe housing of the bearing unit formed integrally with the statorhousing of the spindle motor has an externally threaded projectionprovided on the bottom thereof.

FIG. 42 is a sectional view of another variant of the spindle motoraccording to the present invention.

FIG. 43 is a sectional view of a spindle motor according to the presentinvention, using a bearing unit provided with a static electricitydischarging function.

FIG. 44 is a sectional view of a fifth embodiment of the bearing unitaccording to the present invention, provided with a static electricitydischarging function.

FIG. 45 is a sectional view of a variant of the fifth embodiment ofbearing unit in FIG. 44, provided with a static electricity dischargingfunction.

FIG. 46 is a sectional view of a sixth embodiment of the bearing unitaccording to the present invention, having a thrust bearing formed froma dynamic-pressure fluid bearing.

FIG. 47 is a perspective view of the thrust bearing used in the bearingunit shown in FIG. 46 and having dynamic pressure producing recessesformed therein.

FIG. 48 is a sectional view of a seventh embodiment of the bearing unitaccording to the present invention, including radial and thrust bearingsto support a shaft rotatably and a housing filled with a lubricant andhaving vent paths formed therein, and showing the bearing unit installedin a holder.

FIG. 49 is a perspective view of the bearing unit in FIG. 48, havingvent paths formed therein.

FIG. 50 is a sectional view of an eighth embodiment of the bearing unitaccording to the present invention, having vent paths formed therein.

FIG. 51 is a bottom view of the bearing unit in FIG. 50.

FIG. 52 is a perspective view of a variant of the seventh embodiment ofthe bearing unit in FIG. 48, having vent paths formed therein.

FIG. 53 is a perspective view of another variant of the seventhembodiment of the bearing unit in FIG. 48, having a vent path formedtherein.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the bearing unit according to the present invention andthose of the motor using the bearing unit will be explained withreference to the accompanying drawings.

Prior to proceeding to the explanation of the bearing unit according tothe present invention and motor using the bearing unit, there will bedescribed an electronic apparatus in which a motor using the bearingunit according to the present invention is used as a drive unit. Theelectronic apparatus is a portable computer as an information processingapparatus to process various kinds of information.

The above portable computer is generally indicated with a reference 1.As shown in FIG. 2, the computer 1 includes a display unit 2 to displaya result of information processing and the like, and a main unit 3incorporating an information processing to process various kinds ofinformation. The main unit 3 of the computer 1 has provided thereon akeyboard 5 for use in entering various commands for the computer 1 orvarious kinds of information. A radiator 10 is provided inside thekeyboard 5, as shown. The radiator 10 functions to radiate, to outsidethe computer main unit 3, heat dissipated from an information processingcircuit, such as a CPU, disc drive unit, etc., disposed in the computermain unit 3, and also as a cooling apparatus to cool the inside of thecomputer main unit 3.

The radiator 10 incorporated in the computer main unit 3 is housed in acasing 6 that forms the computer main unit as shown in FIG. 3. Theradiator 10 includes a metallic base 11, a motor 12 installed on thebase 11, a fan 13 driven by the motor 12, a fan case 14 housing the fan13, and a heat sink 15, as shown in FIG. 4.

The base 11 is formed generally like the letter “L”, as shown in FIG. 4.The L-shaped base 11 has installed on one side 11 a at one end thereof aheat-dissipation element 16 that is energized and driven to dissipateheat, such as a CPU (central processing unit). The heat-dissipationelement 16 is installed to the one side 11 a of the 0base 11 on contactwith a heat transfer seal 17.

On the base 11, there are installed nearly in the center of the one side11 a a motor 12 and the fan case 14 housing the fan 13 that is driven bythe motor 12. The fan case 14 has formed therein a circular inlet 18open in a position corresponding to the center of the fan 13 driven bythe motor 12. Also, an opening 19 communicating with the inlet 18 isformed in the bottom of the casing 6 in a position opposite to the inlet18 in the fan case 14. Further, the fan case 14 has formed therein anopening 20 to exhaust air sucked through the inlet 18 to outside.

The heat sink 15 is fixed to the one side 11 a at the other end of thebase 11. The heat sink 15 is a corrugated or fin-shaped one made of ametal excellent in the performance of heat radiation, such as aluminum.The base 11 and fan case 14 also should be desirably formed fromaluminum or iron as a metal superb in the performance of heat radiation.

The base 11 has installed thereto the heat-dissipation element 16 andalso the radiator 10 and heat sink 15, which radiate the heat dissipatedfrom the heat-dissipation element 16 as above. It has formed therein aplurality of screw holes 21 through which there are inserted screws usedto fix the base 11 to the inner surface of the casing 6. The base 11 isfixed to the inner surface of the casing 6 by driving fixing screwsinserted in the screw holes 21 into bosses 22 formed inside the casing6, as shown in FIG. 3.

When the base 11 is installed to the inner surface of the casing 6, theheat sink 15 is positioned opposite to an opening 23 formed in thelateral side of the casing 6, as shown in FIGS. 3 and 4.

When the motor 12 is put into operation and the fan 13 is driven by themotor 12 to rotate in the direction of arrow R1 in FIG. 4, the radiator10 constructed as described above sucks air from outside the radiatorthrough the opening 19 formed in the casing 6 in the direction of arrowD1 in FIGS. 3 and 4, while sucking air into the fan case 14 through theinlet 18. As the fan 13 is rotated, the air thus sucked in the fan case14 is circulated in the direction of arrow D₂ in FIGS. 3 and 4, then inthe direction of arrow D₃ in FIG. 4 through the heat sink 15, andexhausted to outside the casing 6 through the opening 23.

Note that the heat dissipated from the heat-dissipation element 16installed to the base 11 and that is driven is transferred to the heatsink 15 installed to the base 11 via the base 11 formed from the metalexcellent in heat-dissipation performance. At this time, the air suckedfrom outside the casing 6 by the rotating fan 13 of the radiator 10 willflow through between a plurality of fins of the heat sink 15 to radiatethe heat transferred to the heat sink 15 to outside the casing 6 throughthe opening 23.

Next, the motor 12 that drives to rotate the fan 13 of theaforementioned radiator 10 and a bearing unit 30 according to thepresent invention used with the motor 12 will be described in detail.

The motor 12 using the bearing unit 30 includes a rotor 31 and stator32, as shown in FIG. 5.

The stator 32 is provided integrally with an upper plate 14 a of the fancase 14 housing the motor 12 along with the fan 13 driven to rotate bythe motor 12. The stator 32 includes a stator yoke 33, a bearing unit 30according to the present invention, a coil 34 and a core 35 having thecoil 34 wound thereon. The stator yoke 33 may be formed eitherintegrally with the upper plate 14 a or the fan case 14, that is, it maybe formed from a part of the fan case 14 or may be formed separatelyfrom the upper plate 14 a. The stator yoke 33 is formed from iron, forexample. The bearing unit 30 is fixed to a holder 37 formed as acylinder in the center of the stator yoke 33 by press-fitting or bondingor by both.

Note that the holder 37 in which the bearing unit 30 is press-fitted isformed as a cylinder integrally with the stator yoke 33.

The holder 37 formed integrally with the stator yoke 33 has installed onthe outer surface thereof the core 35, having wound thereon the coil 34that is supplied with an exciting current, as shown in FIG. 5.

The rotor 31 included together with the stator 32 in the motor 12 isfixed to a rotating shaft 51 supported rotatably by the bearing unit 30,and thus rotates along with the rotating shaft 51. The rotor 31 includesa rotor yoke 42 and the fan 13 with a plurality of blades 43 rotatingalong with the rotor yoke 42. The blades 43 of the fan 13 are formedintegrally with the rotor yoke 42 by out-sert molding on the outersurface of the rotor yoke 42.

The rotor yoke 42 has a cylindrical portion 42 a, and a ring-shapedrotor magnet 44 is provided on the inner surface of the cylindricalportion 42 a to be opposite to the coil 34 of the stator 32. The rotormagnet 44 is a plastic magnet that is alternately magnetized as N and Spoles circumferentially. The rotor magnet 44 is fixed to the innersurface of the rotor yoke 42 with an adhesive.

The rotor yoke 42 includes a plate portion 42 b having a boss 45 formedin the center thereof, and a through-hole 45 a is formed through theboss 45. The rotating shaft 51 supported in the bearing unit 30 has afixing portion 52 provided at the end thereof. With the fixing portion52 of the rotating shaft 51 being press-fitted into the through-hole 45a in the rotor yoke 42, the rotor yoke 42 is fixed to the rotating shaft51 to be rotatable with the latter.

In the motor 12 constructed as above, when the coil 34 of the stator 32is supplied with an exciting current from a drive circuit providedoutside the motor 12 according to a predetermined pattern of excitation,the rotor 31 is rotated along with the rotating shaft 51 under theaction of the magnetic field developed around the coil 34 and that fromthe rotor magnet 44 at the rotor 31. As the rotor 31 is thus rotated,the fan 13 fixed to the rotor 31 and including the plurality of blades43 also is rotated along with the rotor 31. As the fan 13 is thusrotated, air is sucked from outside the apparatus in the direction ofarrow D1 in FIGS. 3 and 4 through the opening 19 in the casing 6 andcirculated in the direction of arrow D₂, and thus it flows through theheat sink 15 and goes out of the casing 6 through the opening 23. Theair will thus radiate the heat dissipated from the heat-dissipationelement 16 to outside the computer main unit 3, namely, to cool theinside of the computer main unit 3.

As shown in FIGS. 5 and 6, the bearing unit 30 supporting the rotatingshaft 51 of the aforementioned motor 12 includes a radial bearing 55which supports the rotating shaft 51 circumferentially and a housing 56which receives the radial bearing 55.

The radial bearing 55 is formed from a sintered metal to have acylindrical shape. The radial bearing 55 and a lubricant 57, being aviscous fluid and filled in the housing 56, form together adynamic-pressure fluid bearing. The radial bearing 55 has dynamicpressure producing recesses 58 formed in the cylindrical inner surfacethereof that is in contact with the inserted rotating shaft 51. As shownin FIG. 7, each of the dynamic pressure producing recesses 58 formed inthe inner surface of the radial bearing 55 includes pairs of recesses 58a, each pair forming a “V” shape, and a coupling recess 58 b eachcoupling two successive V-shaped pairs of recesses 58 a with each othercircumferentially of the inner surface of the radial bearing 55. In thedynamic pressure producing recesses 58, the V-shape of each pair ofrecesses 58 a is directed at the bottom end thereof in the direction ofrotation R2 of the rotating shaft 51. In this embodiment, the dynamicpressure producing recesses 58 are provided in one pair, upper andlower, in parallel with each other perpendicularly to the axis of thecylindrical radial bearing 55. The number and size of the dynamicpressure producing recesses 58 thus formed in the radial bearing 55 areappropriately selected depending upon the diameter and length of theradial bearing 55.

When the rotating shaft 51 inserted in the radial bearing 55 formed as adynamic-pressure fluid bearing continuously rotates about a center axisC1 in the direction of arrow R2 in FIG. 7, the lubricant 57 filled inthe housing 56 circulates through the dynamic pressure producingrecesses 58 and produces a dynamic pressure between the outer surface ofthe rotating shaft 51 and inner surface of the radial bearing 55 tosupport the rotating shaft 51 being rotated. The dynamic pressure thusproduced minimizes the friction between the rotating shaft 51 and radialbearing 55 and assures a smooth rotation of the rotating shaft 51.

The housing 56 having enclosed therein the radial bearing 55 thatsupports the rotating shaft 51 is shaped to enclose the cylindricalradial bearing 55, as will be seen from FIG. 6. It is a memberintegrally formed by molding a synthetic resin.

As shown in FIG. 6, the housing 56 includes a cylindrical housing body61, a bottom portion 62 formed integrally with the housing body 61 toclose the housing body 61 at one end of the latter, and a top portion 63also formed integrally with the housing body 61. The top portion 63 hasformed in the center thereof a shaft insertion hole 65 through which therotating shaft 51 is received rotatably in the radial bearing 55enclosed in the housing 56. A thrust bearing 66 is formed integrallywith and in the center of the inner surface of the bottom portion 62 ofthe housing 56. The thrust bearing 66 supports the rotating shaft 51received in the radial bearing 55. More specifically, the rotating shaft51 has a bottom end portion 51 a formed at one of thrusting-directionalends thereof, or at the bottom end thereof in this case, and the thrustbearing 66 supports the bottom end portion 51 a of the rotating shaft 51to be rotatable. The thrust bearing 66 is formed from a part of thebottom portion 62 of the housing 56 that is projected inwardly orupwardly in this case. The bottom end portion 51 a of the rotating shaft51 is formed to have a circular or tapered shape, and thus the thrustbearing 66 is formed as a pivot bearing for point-supporting the bottomend portion 51 a of the rotating shaft 51.

By out-sert molding of a synthetic resin onto the cylindrical radialbearing 55 into the housing 56 constructed as above, the radial bearing55 is formed integrally inside the housing 61.

The synthetic resin used to mold the housing 56 is not limited to anyspecial one but should desirably be one which will increase the angle ofcontact when repelling the lubricant 57 filled in the housing 56. Sincethe housing 56 has the thrust bearing 66 formed integrally therewith, itshould desirably be formed from a synthetic resin excellent inlubricity. Therefore, the housing 56 should preferably be formed from afluorinated synthetic resin, such as polyimide, polyamide, polyacetal orthe like, or a synthetic resin such as polytetrafluoroethylene teflon,nylon or the like. Further, a synthetic resin such as PC(polycarbonate), ABS (acrylonitrile butadiene styrene) or the like maybe used for this purpose. Moreover, the housing 56 may be formed from aliquid crystal polymer that can be molded with an extremely highaccuracy.

Thus, the rotating shaft 51 is rotatably supported in the radial bearing55 enclosed in the housing 56 and on the thrust bearing 66 formedintegrally with the housing 56. The rotating shaft 51 includes a shaftportion 51 b in addition to the aforementioned bottom end portion 51 a.The bottom end portion 51 a supported on the thrust bearing 66 is formedcircular or tapered as mentioned above. The rotating shaft 51 also hasformed at the other end (top end) thereof a fixing portion 52 to whichthe rotor 31 of a rotating body, for example, of the motor 12, is fixed.It should be noted that the shaft body 51 b and fixing portion 52 areformed to have the same diameter.

As shown in FIG. 6, the rotating shaft 51 is supported at the bottom endportion 51 a thereof on the thrust bearing 66, while the shaft body 51 bis supported at the outer surface thereon on the radial bearing 55, withthe fixing portion 52 provided at the other end (top end) of therotating shaft 51 being projected to outside through the shaft insertionhole 65 formed in the top portion 63 of the housing 56.

Note that the shaft insertion hole 65 is formed to have a somewhatlarger diameter than the outside diameter of the shaft body 51 b, sothat the rotating shaft 51 inserted through the shaft insertion hole 65can be rotated with no contact or friction with the inner surface of theshaft insertion hole 65. More specifically, the shaft insertion hole 65is formed to define between the inner surface thereof and outer surfaceof the shaft body 51 b a gap 69 whose width c is sufficient to preventthe lubricant 57 filled in the housing 56 from leaking out of thehousing 56. As seen from the foregoing, an oil sealing is provided bythe top portion 63 of the housing 56 in which there is formed the shaftinsertion hole 65 defining, along with the outer surface of the rotatingshaft 51, the gap 69 whose width is sufficient to prevent the leakage oflubricant 57 filled in the housing 56.

Because the top portion 63 formed integrally with the housing body 61 isformed from a synthetic resin such as polyimide, polyamide or nylon, itassures an angle of about 60 deg., at which the inner surface of theshaft insertion hole 65 is in contact with the lubricant 57. The bearingunit 30 according to the present invention thus assures a larger angleof contact of the lubricant 57 with the inner surface of the shaftinsertion hole 65 in the top portion 63 of the housing 56, withouthaving to apply any surfactant to the top portion 63 providing the oilsealing and including the inner surface of the shaft insertion hole 65.Hence, the lubricant 57 can be prevented from leaking to outside thehousing 56 through the shaft insertion hole 65 by a centrifugal forcedeveloped as the rotating shaft 51 rotates.

Further, the rotating shaft 51 is tapered (as indicated at a reference67) at a surface portion thereof opposite to the inner surface of theshaft insertion hole 65. The tapered portion 67 increases the gap 69defined between the outer surface of the rotating shaft 51 and the innersurface of the shaft insertion hole 65 outwardly of the housing 56. Thetapered portion 67 imparts a pressure gradient in the gap 69 definedbetween the outer surface of the rotating shaft 51 and the inner surfaceof the shaft insertion hole 65 such that there will develop a force tocause the lubricant 57 filled in the housing 56 to move inwardly of thehousing 56. Since the lubricant 57 is thus moved inwardly of the housing56 when the rotating shaft 51 rotates, it will positively enter thedynamic pressure producing recesses 58 in the radial bearing 55 formedfrom a dynamic-pressure fluid bearing to produce a dynamic pressurewhich will assure a stable supporting of the rotating shaft 51 andprevent the lubricant 57 filled in the housing 56 from leaking out ofthe latter.

In the bearing unit 30 according to the present invention, the lubricant57 entering the dynamic pressure producing recesses 58 formed in theradial bearing 55 formed from the dynamic-pressure fluid bearing toproduce a dynamic pressure is filled into the housing 56 up to the gap69 defined between the tapered portion 67 of the rotating shaft 51 andthe inner surface of the shaft insertion hole 65, as shown in FIGS. 6and 8. That is, the lubricant 57 is filled into clearances inside thehousing 56 and further impregnated into the radial bearing 55 formedfrom a sintered metal.

The gap 69 defined between the tapered portion 67 of the rotating shaft51 and the inner surface of the shaft insertion hole 65 will further bedescribed hereinbelow. The minimum width of the gap 69 is equivalent tothe width c defined between the outer surface of the rotating shaft 51and the inner surface of the shaft insertion hole 65. The width c of thegap 69 should desirably be 20 to 200, and more preferably should be onthe order of 100 μm. If the width c of the gap 69 is smaller than 20 μm,it is difficult to mold a synthetic resin into an integrally formedhousing 56 of the bearing unit 30 with a high accuracy. Also, if thewidth c of the gap 69 is larger than 200 μm, when a shock is applied tothe bearing unit 30, the lubricant 57 filled in the housing 56 will flyout of the housing 56, namely, the shock resistance of the housing 56will be lower.

The above shock resistance will be indicated with a symbol G. The shockresistance G is given by a following equation (1):G=(12γ cos β/2ρc ²)/g  (1)

-   -   where γ: Surface tension of the lubricant        -   β: Angle of contact of the lubricant        -   ρ: Density of the lubricant        -   c: Gap between the rotating shaft and shaft insertion hole        -   g: Free-fall speed

As seen from the above equation (1), the shock resistance G is inverselyproportional to the width c of the gap 69.

Also, a thermal expansion-caused rise of the lubricant level, indicatedwith a symbol h, is given by a following equation (2):h=VαΔt/2πRc  (2)

-   -   where V: Filled amount of the lubricant        -   α: Thermal expansion coefficient        -   Δt: Temperature change        -   R: Radius of the rotating shaft

As known from the equation (2), the rise h of the lubricant level isinversely proportional to the magnitude of the width c. So, in the casewhere the width c is decreased, the shock resistance G is improved butthe level of the lubricant 57 will be caused to violently rise due to atemperature elevation, and thus the shaft insertion hole 65 will have tobe deeper axially of the housing 56.

The results of calculation show that in the bearing unit 30 having therotating shaft 51 having a diameter of 2 to 3 mm, when the width c ofthe gap 69 defined between the outer surface of the rotating shaft 51and the inner surface of the shaft insertion hole 65 is on the order of100 μm and the shaft insertion hole 65 is about 1 mm deep (H₁), thehousing 56 will have a sock resistance more than 1000 G and a thermalresistance of 80° C. In this case, the bearing unit 30 can prevent thelubricant 57 filled in the housing 56 from flying out of the latter, andthus it is highly reliable.

Further, since in the bearing unit 30, the tapered portion 67 of therotating shaft 51 increases the width c of the gap 69 defined betweenthe outer surface of the rotating shaft 51 and the inner surface of theshaft insertion hole 65 outwardly of the housing 56, there will takeplace a pressure gradient in the width c of the gap 69 defined betweenthe outer surface of the rotating shaft 51 and the inner surface of theshaft insertion hole 65, such that under a centrifugal force developedwhen the rotating shaft 51 rotates, there will take place a force withwhich the lubricant 57 filled in the housing 56 is moved inwardly of thelatter.

That is, in the bearing unit 30 according to the present invention, thegap 69 defined between the outer surface of the rotating shaft 51 andthe inner surface of the shaft insertion hole 65 provides a surfacetension seal to prevent the lubricant 57 from flying out of the housing56.

The surface tension seal will further be described below. The surfacetension seal is a technique using the capillary phenomenon of a fluid. Arise h of a fluid through a capillary tube, as shown in FIG. 9, is givenby a following equation (3):2πrγ cos θ=mg  (3)

The term m in the above equation (3) is given by a following equation(4):m=πr²hρ  (4)

-   -   where m: Fluid mass within range of rise h inside the capillary        tube        -   r: Radius of the capillary tube        -   γ: Surface tension of a viscous fluid        -   θ: Angle of contact of the viscous fluid        -   ρ: Density of the viscous fluid        -   g: Gravitational acceleration

A following equation (5) is derived from equations (3) and (4):h=2γ cos θ/rρg  (5)

Generally, the relation between a suction pressure P and level of afluid is given by a following equation (6):P=ρgh  (6)

The suction pressure P can be given by the following equation (7) basedon equations (5) and (6):P=2γ cos θ/r  (7)

In equation (7), the suction pressure P means a pressure under which thefluid is moved inwardly of the housing 56. It will be known fromequation (7) that the suction pressure P will be higher with thecapillary tube being larger in diameter.

The explanation applies for a capillary tube whose section is circular.In the bearing unit 30, however, the lubricant 57 having entered the gap69 defined between the outer surface of the rotating shaft 51 and theinner surface of the shaft insertion hole 65 has a toroidal section asshown in FIG. 10. In this case, the rise h1 of the lubricant 57 as fluidthrough the capillary tube is given by the following equation (8):2π(R+r)γ cos θ=mg  (8)

The term m in the equation (8) is given by the following equation (9):m=π(R ² −r ²)hρ  (9)

The following equation (10) is derived from the equations (8) and (9):h ₁=(2γ cos θ)/((R−r)ρg)  (10)

On the assumption that the term (R−r) is the width c of the gap 69defined between the outer surface of the rotating shaft 51 and the innersurface of the shaft insertion hole 65, the equation (10) will be givenby the following equation (11):h=(2γ cos θ)/(cρg)  (11)

Therefore, in case the section of the lubricant 57 is toroidal, thesuction pressure P is given by the following equation (12):P=2γ cos θ/c  (12)

When the width c of the gap 69 defined between the outer surface of therotating shaft 51 and the inner surface of the shaft insertion hole 65is 0.02 cm (0.2 mm), the surface tension γ of a viscous fluid is 30dyn/cm² and the contact angle θ of the lubricant 57 is 15°, and thesuction pressure P is determined by the following equation (13) to be2.86×10⁻³ (atm):P=2×30×cos 15°/0.02=3.00×10³ dyn/cm²=2.86×10⁻³(atm)  (13)

As known from the above equation (12), the suction pressure P will behigher when the width c of the gap 69 is smaller. Therefore, the taperedportion 67 of the rotating shaft 51 will permit the lubricant 57 to moveas a viscous fluid in the direction in which the width c of the gap 69is smaller, that is, inwardly of the housing 56.

It is assumed here that, as shown in FIG. 11, the tapered portion 67 ofthe rotating shaft 51 has portions t1 and t2 different in diameter fromeach other, for example. In this case, since a gap c1 defined betweenthe outer surface of the rotating shaft 51 and the inner surface of theshaft insertion hole 65 and taken at the level of the portion t1 and agap c2 defined between the outer surface of the rotating shaft 51 andthe inner surface of the shaft insertion hole 65 and taken at the levelof the portion t2 are in such a relation that c1<c2, so suctionpressures P1 and P2 at the portions t1 and t2 are in such a relationthat P1>P2 and the suction pressure P forcing the lubricant 57 inwardlyof the housing 56 increases as the width c of the gap 69 defined betweenthe outer surface of the rotating shaft 51 and the inner surface of theshaft insertion hole 65 is smaller, as will be known from the equation(12).

Thus, by forming the tapered portion 67 of the rotating shaft 51 suchthat the width c of the gap 69 defined between the outer surface of therotating shaft 51 and the inner surface of the shaft insertion hole 65,and which defines such an oil seal as prevents the lubricant 57 filledin the housing 56 from leaking out of the housing 56, is smallerinwardly of the housing 56, a pressure gradient will develop in thelubricant 57 in the gap 69 defined between the outer surface of therotating shaft 51 and the inner surface of the shaft insertion hole 65.That is, the pressure gradient imparted to the lubricant 57 will belarger inwardly of the housing 56 in which direction the width c of thegap 69 is smaller. Since the suction pressure P forcing the lubricant 57inwardly of the housing 56 is always acting on the lubricant 57 becauseof such a pressure gradient developed in the lubricant 57, the lubricant57 staying in the gap 69 will have no air mixed therein even when therotating shaft 51 rotates.

In case the tapered portion 67 is not formed on the rotating shaft 51,namely, when the width c of the gap 69 defined between the outer surfaceof the rotating shaft 51 and the inner surface of the shaft insertionhole 65 has the diameter thereof not changed along the depth of theshaft insertion hole 65, as shown in FIG. 12, no pressure gradient willdevelop in the lubricant 57 having entered the gap 69 defined betweenthe outer surface of the rotating shaft 51 and the inner surface of theshaft insertion hole 65, so that the lubricant 57 will stay uniformly inthe gap 69. That is to say, the gap 69 defined between the outer surfaceof the rotating shaft 51 and the inner surface of the shaft insertionhole 65 works as an oil seal when its width c is reduced. The lubricant57 having entered the gap 69 having such a reduced width c will moveinside the gap 69 and have air E mixed therein as the case may be. Ifthe lubricant 57 has air E mixed therein, the air E will be expanded dueto a temperature change, barometric pressure change, etc. and cause thelubricant 57 to fly out of the housing 56 through the gap 69 forming theoil seal.

On the contrary, by forming the tapered portion 67 of the rotating shaft51 so that the width c of the gap 69 defined between the outer surfaceof the rotating shaft 51 and the inner surface of the shaft insertionhole 65 is smaller inwardly of the housing 56 as in the bearing unit 30according to the present invention, such a pressure gradient that thepressure will be higher inwardly of the housing 56 will take place inthe lubricant 57 having entered the gap 69, and so the lubricant 57 canbe prevented from having the air E mixed therein when the rotating shaft51 rotates.

Further, the tapered portion 67 of the rotating shaft 51 prevents thelubricant 57 having entered the gap 69 defined between the outer surfaceof the rotating shaft 51 and the inner surface of the shaft insertionhole 65 from flying outwardly of the housing 56 and moves the lubricant57 to the entire outer surface of the rotating shaft 51 even when therotating shaft 51 becomes eccentric with respect to the shaft insertionhole 65 formed in the housing 56. Thus, it is possible to prevent thelubricant 57 on the circumference of the rotating shaft 51 from runningshort and assure a stable rotation of the rotating shaft 51.

In case the rotating shaft 51 has not the aforementioned tapered portion67, if the rotating shaft 51 becomes eccentric with respect to the shaftinsertion hole 65 in the housing 56, the lubricant 57 will concentrateto the gap portion, whose width c is smaller, defined between the outersurface of the rotating shaft 51 and the inner surface of the shaftinsertion hole 65, while it will be cut in the gap portion whose width cis larger and thus have air E mixed therein, as shown in FIG. 13. Theair E mixed in the lubricant 57 will be expanded due to any temperaturechange, barometric pressure change or the like and thus cause thelubricant 57 to fly outwardly of the housing 56 through the gap 69forming the air seal.

On the other hand, in case the rotating shaft 51 is shaped to have thetapered portion 67 as in the bearing unit 30 according to the presentinvention, even if the rotating shaft 51 becomes eccentric with respectto the shaft insertion hole 65 in the housing 56, the gap 69 of the samewidth c is defined on the elliptic trajectory along which the eccentricrotating shaft 51 rotates, as shown in FIG. 14, and the width c of thegap 69 defined between the outer surface of the rotating shaft 51 on theelliptic trajectory and the inner surface of the shaft insertion hole 65is constant all around the rotating shaft 51 as shown in FIG. 15. So,the lubricant 57 will not concentrate to the gap 69 of the smaller widthc. Thus, the lubricant 57 can be prevented from flying out of the gap 69and, hence, out of the housing 56.

In the above bearing unit 30, the rotating shaft 51 includes the taperedportion 67, but the inner surface of the shaft insertion hole 65 in thehousing 56 may be tapered (indicated at a reference 68) as shown in FIG.16.

Next, the production process for the bearing unit 30 according to thepresent invention, constructed as above, will be described.

To produce the bearing unit 30 according to the present invention, thehousing 56 is formed on the outer surface of the radial bearing 55 byout-sert molding of a synthetic resin. At this time, the thrust bearing66 is integrally inside the housing 56. More specifically, when thehousing 56 is formed by the out-sert molding, the radial bearing 55 isjoined to the inner surface of the housing 56 and securely held in placebetween the top and bottom portions 63 and 62 formed integrally on thetop and bottom, respectively, of the cylindrical housing body 61. Thus,the radial bearing 55 is fixed in place.

Next, the rotating shaft 51 is introduced into the housing 56 throughthe shaft insertion hole 65 formed in the top portion 63 of the housing56. Namely, the rotating shaft 51 is inserted into the radial bearing 55down to the thrust bearing 66 formed on the bottom portion 62 of thehousing 56. The rotating shaft 51 thus supported at the bottom endportion 51 a thereof on the thrust bearing 66 and in the radial bearing55 is received rotatably in the housing 56.

After the rotating shaft 51 is inserted in the housing 56, the lubricant57 is filled into the housing 56. For this filling of the lubricant 57,the housing 56 having the rotating shaft 51 inserted therein is immersedin the lubricant 57 in a bath, and then the lubricant bath in which thehousing 56 is placed is put into a vacuumization apparatus in which itis vacuumized. After completion of the vacuumization, the lubricant bathis taken out of the vacuumization apparatus into the atmosphere. Thelubricant 57 is thus filled in the housing 56.

The lubricant 57 thus filled in the housing 56 will not leak out of thehousing 56 through the shaft insertion hole 65, even when it is expandeddue to a temperature change, and will not run short in the gap 69defined between the rotating shaft 51 and the inner surface of the shaftinsertion hole 65, even when it is shrunk due to a temperature change.Namely, the lubricant 57 will always keep a level within the depth ofthe shaft insertion hole 65, even when the ambient temperature varies.

By filling the lubricant 57 into the housing 56 through theabove-mentioned vaccumization of the lubricant bath in the vacuumizationapparatus, the internal pressure of the housing 56 will be lower thanthe external one. As a result, the lubricant 57 will be prevented fromeasily leaking out of the housing 56.

Since the bearing unit 30 according to the present invention has theradial bearing 55 thereof made of a sintered metal, the radial bearing55 is filled with the lubricant 57, and also the dynamic pressureproducing recesses 58 formed in the inner surface of the radial bearing55 are filled with the lubricant 57. When the rotating shaft 51 rotates,the dynamic pressure producing recesses 58 will produce a dynamicpressure. Namely, the housing 56 has the lubricant 57 filled in all gapstherein.

The aforementioned bearing unit has the housing thereof formed from asynthetic resin by molding. However, the material of the housing is notlimited to any special synthetic resin, but it may be a synthetic resincontaining a metallic material moldable in a mold tool or any othermolding material. It should be noted that when the housing is formedfrom any other material than a synthetic resin, any appropriate angle ofcontact of the lubricant filled in the housing with the inner surface ofthe through-hole formed in the housing may not possibly be maintained.In such a case, however, it suffices to provide a larger angle ofcontact by applying a surfactant to the inner surface of thethrough-hole formed in the housing and also to the outer surface of thetop portion including the inner surface of the through-hole.

In the aforementioned bearing unit, the thrust bearing is formed as apart of the housing. However, the bottom portion of the housing wherethe thrust bearing is formed may be formed independently of the housingbody and may be joined to the housing body by heat or ultrasonicsealing.

Next, there will be described a variant of the bearing unit that isconstructed by first forming, independently of a housing body, a housingbottom portion having a thrust bearing formed thereon, and then joiningit to the housing body.

Note that in the following explanation and illustration, the same orsimilar elements of the bearing unit as those of the aforementionedbearing unit 30 will be indicated with the same or similar references asthose used in the illustration and explanation of the beating unit 30and will not be described in detail any longer.

The second embodiment of the bearing according to the present inventionis generally indicated with a reference 70. The bearing unit 70 includesa housing 71 consisting of two members: a housing body 72 formed toreceive a radial bearing 55 designed as a dynamic-pressure fluidbearing, and a housing bottom closer 73, having a thrust bearing 66formed integrally thereon, as shown in FIG. 17. Similar to the housingbody 61 of the aforementioned bearing unit 30, the housing body 72 isformed by out-sert molding of a synthetic resin on the outer surface ofthe radial bearing 55, and has formed in the center of the top portion63 the shaft insertion hole 65 through which the rotating shaft 51 isintroduced into the radial bearing 55 in which it will be supportedrotatably. According to this second embodiment, the housing body 72 hasthe bottom portion 75 formed at the bottom thereof and in which there isformed a through-hole 74 through which the thrust bearing 66 provided onthe housing bottom closer 73 is projected inwardly of the housing body72. Thus, the radial bearing 55 enclosed in the housing body 72 issecurely held in place between the top and bottom portions 63 and 75.

The housing bottom closer 73 joined to the housing body 72 has formedthereon the inwardly projecting thrust bearing 66 that supports acircular or tapered bottom end portion 51 a of the rotating shaft 51inserted in the radial bearing 55. The thrust bearing 66 serves as apivot bearing for point-supporting of the bottom end portion 51 a of therotating shaft 51. With the thrust bearing 66 being projected inwardlyof the housing body 72 through the through-hole 74, a peripheral fixingportion 76 around the thrust bearing 66, namely, a portion of thehousing bottom closer 73 not including the thrust bearing 66, is weldedto the bottom portion 75 of the housing body 72. The housing bottomcloser 73 welded to the bottom portion 75, namely, to the housing body72, seals the through-hole 74 in the bottom portion 75. Thus, thehousing 71 has a sealed structure except for the shaft insertion hole 65having the rotating shaft 51 inserted therein to provide an oil seal.

The housing bottom closer 73 is joined by ultrasonic welding of thefixing portion 76 to the bottom portion 75 of the housing body 72. Theside of the fixing portion 76 to be welded to the bottom portion 75 hasprovided a ring-shaped energy director whose section is triangular. Withthe energy director set to abut the bottom portion 75, the housingbottom closer 73 is combined with the housing body 72. This assembly isset in an ultrasonic welding apparatus. In this condition, an ultrasoundtransducer of the ultrasound welding apparatus emits an ultrasoundoscillation from the side of the housing bottom closer 73. Theultrasound oscillation is concentrated to the energy director, whichwill thus be melted to weld the housing bottom closer 73 to the housingbody 72.

By forming the housing body 72 and the housing bottom closer 73 havingthe thrust bearing 66 formed thereon independently of each other, it ispossible to form the housing body 72 and housing bottom closer 73 fromappropriate materials for their respective functions, respectively. Thehousing body 72, having the top portion 63 in which the shaft insertionhole 65 forming an oil seal is formed, should desirably be formed with ahigh precision. To this end, the housing body 72 is formed from a liquidcrystal polymer that can be molded with a high precision of molding,while the housing bottom closer 73 having the thrust bearing 66 formedintegrally therewith is formed from a polytetrafluoroethylene teflonthat is a fluorinated synthetic resin having a high slidability andsufficient mechanical strength, such as polyimide, polyamide, polyacetalor the like. It should be noted that both the housing body 72 andhousing bottom closer 73 may be formed from the liquid crystal polymer.The liquid crystal polymer is a resin superb in rotational slidability,and thus it is ideal for use as the material of the housing bottomcloser 73 having the thrust bearing 66 formed integrally therewith.

The housing bottom closer 73 may be formed on the housing body 72 havingbeen formed over the radial bearing 55 to form the housing 71 by theout-sert molding. Thus, the housing bottom closer 73 is integral withthe housing body 72. In this case, the housing bottom closer 73 isformed from a synthetic resin that is moldable at a temperature lowerthan the highest temperature the synthetic resin material of the housingbody 72 can withstand, for the housing body 72 should be prevented frombeing expanded and damaged by the molding temperature or the precisionof molding should be maintained when forming the housing bottom closer73 on the housing body 72 by the out-sert molding.

In the aforementioned bearing units 30 and 70 according to the presentinvention, the rotating shaft 51 is formed from a metal, and the bottomend portion 51 a of the rotating shaft 51, supported on the thrustbearing 66, is formed circular or tapered. That is, the thrust bearing66 is formed as a pivot bearing. Therefore, the thrust bearing 66preferably should be formed from a metal superb in slidability andabrasion resistance.

FIG. 18 is an axial-sectional view of a variant of the aforementionedbearing unit 70. In case the thrust bearing 66 is formed from a metal, asynthetic resin is molded, by the insert molding, onto the metallicthrust bearing 66 to form the housing bottom closer 73. The housingbottom closer 73 is joined by ultrasonic welding to the housing body 72.Thus, it is integral with the housing body 72.

The bearing unit according to the present invention desirably should bedesigned to prevent the rotating shaft from coming off the housing, inorder to ensure a stable rotation of the rotating shaft.

The bearing unit provided with a come-off preventive mechanism toprevent the rotating shaft from coming off the housing will be describedhereinbelow:

Note that in the following illustration and explanation, the same orsimilar elements of the bearing unit as those of the bearing unit 30shown in FIGS. 5 and 6 will be indicated with the same or similarreferences as those in FIGS. 5 and 6 and will not be explained in detailany longer.

The bearing unit provided with a come-off preventive mechanism is shownas a third embodiment of the present invention in FIG. 19. It isgenerally indicated with a reference 80. As shown, the bearing unit 80includes a housing 81 composed of a housing body 82 having the radialbearing 55 encased therein and a shaft end receptacle 83 in which thethrust bearing 66 is received. The shaft end receptacle 83 includes ahousing bottom closer 84 having the thrust bearing 66 formed integrallytherewith. The shaft end receptacle 83 is coupled integrally to thehousing body 82 to form the housing 81. The housing 81 also is formedfrom a synthetic resin similarly to the aforementioned bearing units 30and 70.

The housing body 82 has a shaft retainer 86 formed integrally at thebottom thereof to which the shaft end receptacle 83 is coupled. Theshaft retainer 86 has formed in the center thereof a through-hole 85 inwhich there is inserted one end of the rotating shaft 51, on which thebottom end portion 51 a is formed. The through-hole 85 has a diametersmaller than the radius R1 of the rotating shaft 51 received in thehousing 81. The shaft retainer 86 cooperates with the top portion 63 ofthe housing body 82 to support the radial bearing 55 encased in thehousing body 82.

On the other hand, the rotating shaft 51 has formed in a portion thereofan engagement groove 87 in which the shaft retainer 86 is engaged whenthe rotating shaft 51 is introduced into the housing 81.

The rotating shaft 51 is inserted first at the bottom end portion 51 athereof into the housing 81 until the bottom end portion 51 a is seatedon the thrust bearing 66. Then, the shaft retainer 86 is engaged in theengagement groove 87. More specifically, the shaft retainer 86 iselastically deformed as the bottom end portion 51 a of the rotatingshaft 51 is inserted into the through-hole 85. Then, the rotating shaft51 is inserted until it is seated at the bottom end portion 51 a thereofon the thrust bearing 66. Then, the shaft retainer 86 is aligned withthe engagement groove 87 whose diameter is smaller than the former. Theshaft retainer 86 having been elastically deformed as above iselastically restored to its initial condition and engaged into theengagement groove 87. Since the shaft retainer 86 is thus engaged in theengagement groove 87, the rotating shaft 51 is limited from moving inthe direction of arrow X₁ in FIG. 19 and thus prevented from coming offthe housing 81.

In this embodiment, the housing 81 may be formed by out-sert molding ofthe shaft end receptacle 83 on the housing body 82 made of a syntheticresin. Also, the housing 81 may be joined by thermal ultrasonic weldingof the synthetic resin-made shaft end receptacle 83 to the syntheticresin-made housing body 82.

FIG. 20 shows a fourth embodiment of the bearing unit according to thepresent invention. It is provided with a come-off preventive mechanismto prevent the rotating shaft from coming off the housing.

Note that in the following illustration and explanation, the same orsimilar elements of the bearing unit as those of the bearing unit 30shown in FIGS. 5 and 6 will be indicated with the same or similarreferences as those in FIGS. 5 and 6 and will not be explained indetail.

The bearing unit is generally indicated with a reference 90. As shown inFIG. 20, the bearing unit 90 is provided with a come-off preventivemechanism to prevent the rotating shaft from coming off the housing. Thecome-off preventive mechanism is provided at the side of the housing 56where the rotating shaft 51 projects. The bearing unit 90 has a shaftend receptacle 92 provided on the top portion 63 having the shaftinsertion hole 65 in which the rotating shaft 51 is inserted and thusforming an oil seal.

The shaft end receptacle 92 is formed coupled integrally to the housing56. The shaft end receptacle 92 has a shaft retainer 96 formedintegrally on the top thereof and which has a through-hole 95 in whichthe rotating shaft 51 is inserted. The through-hole 95 is formed to havea diameter smaller than the diameter R₁ of the rotating shaft 51received in the housing 56. The shaft retainer 96 is formed from asynthetic resin similarly to the housing 56 and thus elasticallydeformable.

On the other hand, there is formed in the outer end portion of therotating shaft 51 where the fixing portion 52 is provided an engagementgroove 97 into which the shaft retainer 96 is engaged when the rotatingshaft 51 is introduced into the housing 56. When the rotating shaft 51is inserted first at the bottom end portion 51 a thereof into thehousing 56 until the bottom end portion 51 a abuts the thrust bearing66, the shaft retainer 96 is engaged into the engagement groove 97formed in the fixing portion 52 projected out of the housing 56. Moreparticularly, the shaft retainer 96 is elastically deformed as therotating shaft 51 is inserted into the through-hole 95. When therotating shaft 51 is inserted until the bottom end portion 51 a thereofis seated on the thrust bearing 66, the shaft retainer 96 is alignedwith the engagement groove 97 whose diameter is smaller than the former.The shaft retainer 96 having been elastically deformed as above iselastically restored to its initial condition and engaged into theengagement groove 97. Since the shaft retainer 96 is thus engaged in theengagement groove 97, the rotating shaft 51 is limited from moving inthe direction of arrow X₁ in FIG. 20 and thus prevented from coming offthe housing 56.

In this embodiment, the synthetic resin-made shaft end receptacle 92made of a synthetic resin can be formed by out-sert molding on thesynthetic resin-made housing 56 Also, the shaft end receptacle 92 may bejoined by thermal or ultrasonic welding to the synthetic resin-madehousing 56.

Note here that the bearing unit according to the present invention andmotor using the bearing unit can be used as the drive unit in a computerradiator previously described and also as a spindle motor that drives torotate a hard disc used as a recording medium in a disc drive unit.

A disc drive unit using a motor that uses the bearing unit according tothe present invention will be described hereinbelow:

The disc drive unit is a one installed in a PC card slot of anotebook-sized personal computer. It is designed very small and thin.

FIGS. 21 to 23 show together the disc drive unit in which the motoraccording to the present invention is used. The disc drive unit isgenerally indicated with a reference 101. As shown, the disc drive unit101 includes a casing 102 as the main body, a hard disc 103 being amagnetic recording medium disposed in the casing 102, a spindle motor104 using the bearing unit according to the present invention and whichdrives to rotate the hard disc 103, magnetic heads 105 which scan thesignal recording area of the hard disc 103 being rotated by the spindlemotor 104 to write or read information signals to or from the hard disc103, and a rotating actuator 106 to support the magnetic heads 105.

The casing 102 is formed from a pair of casing halves 102 a and 102 b,upper and lower, by joining them end to end.

The hard disc 103 is fixed to a rotor 115 of the spindle motor 104 asshown in FIG. 24, and rotates along with the rotor 115.

The rotating actuator 106 supporting the magnetic heads 105 which scanthe hard disc 103, includes a pair of head support arms 107 extendingover each side of the hard disc 103, and a voice coil 108. The voicecoil 108 is provided between a pair of magnets 109 disposed inside thecasing 102 as shown in FIG. 23. The voice coil 108 and magnets 109 formtogether a voice coil motor. When the rotating actuator 106 is suppliedat the voice coil 108 thereof with an exciting current, a magnetic fielddeveloped around the voice coil 108 and magnetic fields developed aroundthe pair of magnets 109 act on each other to produce an electromagneticforce with which the head support arms 107 are rotated about a pivot 111in the directions of arrows F1 and F2 shown in FIGS. 21 and 22. As thehead support arms 107 are rotated by the voice coil motor, the magneticheads 105 supported by the head support arms 107, respectively, arepositioned on an arbitrary recording track on the hard disc 103 beingrotated and write an information signal to the hard disc 103 or read aninformation signal already recorded in the hard disc 103. It should benoted that each of the magnetic heads 105 is one using amagneto-resistive element.

Note that the disc drive unit 101 is provided at one end of the casing102 with a connection terminal 112 which provides an electricalconnection to a computer or the like. Inside the casing 102, there areprovided a system LSI (large-scale integrated circuit) 113 and a circuitboard 114 having mounted thereon ordinary electronic parts such as IC(integrated circuit), etc.

The spindle motor 104 to rotate the hard disc 103 is provided with arotor 115 and stator 116.

The rotor 115 includes a rotor housing 120 having formed thereon aturntable 117 on which the hard disc 103 is mounted, a chucking member118 working with the turntable 117 to clamp the hard disc 103, and arotor magnet 119.

Note that the rotor 115 has the rotor housing 120 thereof supportedrotatably by the bearing unit 30 according to the present invention,having been described in the foregoing. Since the basic construction ofthe bearing unit 30 used in the spindle motor 104 is as has beendescribed in the foregoing, it will not be described in detail anylonger.

The rotor housing 120 is formed from a magnetic material, such as iron,and has a fitting hole 126 formed in the center thereof. The rotorhousing 120 is press-fitted at the fitting hole 126 thereof on thefixing portion 52 of the rotating shaft 51. Thus, the rotor housing 120is rotated along with the rotating shaft 51 of the bearing unit 30.

As shown in FIG. 24, the turntable 117 is formed protruded from theperimeter of the rotor housing 120. It receives the hard disc 103. Thehard disc 103 is supported at the inner circumferential portion thereofby the turntable 117 and chucking member 118 forced to the turntable 117to be rotatable along with the rotor housing 120. It should be notedthat the chucking member 118 is formed like a ring from a stainlesssteel, for example.

The rotor magnet 119 provided on the cylindrical inner surface of therotor housing 120 is formed like a ring and alternately magnetized as Nand S poles circumferentially. The rotor magnet 119 is formed from asintered neodymium-iron-boron (Nd—Fe—B), for example.

The stator 116 included together with the rotor 115 in the spindle motor104 includes a stator housing 121, a housing 56 of the bearing unit 30,an excitation coil 122, an iron core 123 on which the excitation coil122 is wound, and a flexible printed wiring board (not shown) havingmounted thereon a drive circuit to control the rotation of the spindlemotor 104, etc.

The stator housing 121 is made of a stainless steel, for example, andhas the flexible printed wiring board fixed thereto by bonding. Theflexible printed wiring board is electrically connected to theexcitation coil 122. The excitation coil 122 has U-, V- and W-phaseterminals and a common terminal thereof led out of the stator housing121 via the flexible printed wiring board. The flexible printed wiringboard is electrically connected to an excitation controller 125 via aconnector.

The iron core 123 having the excitation coil 122 wound thereon has ninepoles, for example. On the other hand, the rotor magnet 119 has, forexample, twelve poles, including the N and S poles, formedcircumferentially. When the excitation coil 122 is supplied with anexciting current in a predetermined pattern of excitation from theexcitation controller 125, a magnetic field developed around theexcitation coil 122 thus excited and magnetic fields developed aroundthe rotor magnet 119 pair of magnets 109 act on each other tocontinuously rotate the rotor 115 about the rotating shaft 51 inrelation to the stator 116.

The stator housing 121 has a cylindrical portion 130 formed to rise fromit. The bearing unit 30 is inserted at the housing 56 thereof in thecylindrical portion 130. That is, the cylindrical portion 130 securesthe bearing unit 30.

Note that the bearing unit 30 supports the rotor 115 at the top of therotating shaft 51 thereof and is installed in the stator housing 121,whereby it forms a part of the spindle motor 104. The bearing unit 30has to be positioned for accurate installation to the stator housing121. For supporting the bearing unit 30 in the stator housing 121, thebearing unit 30 has a step 131 formed as an engagement means on thehousing 56 thereof, as shown in FIGS. 24 and 25. The bearing unit 30 isengaged at the step 131 on the stator housing 121. The step 131 isformed on the outer surface of the housing 56 where there is providedthe top portion 63 through which the rotating shaft 51 projects out.

Note that the cylindrical portion 130 of the stator housing 121 includedin the stator 116 of the spindle motor 104 thus retains the syntheticresin-made housing 56 of the bearing unit 30.

With the bearing unit 30 having the step 131 as an engagement meansformed on the housing 56 as above being inserted into the cylindricalportion 130 provided on the stator housing 121 made of a metal, such asa stainless steel, the cylindrical portion 130 is riveted at the topthereof (indicated at a reference 132) to engage on the step 131,whereby the rotating shaft 51 is positively secured in the statorhousing 121. By thus forming the to-be-riveted portion 132 at thecylindrical portion 130 in which the housing 56 of the bearing unit 30is inserted, it is possible to install the bearing unit 30 in place to amotor, such as the spindle motor, without applying any large load to thebearing unit 30.

The synthetic resin, such as polyimide, polyamide or nylon, used to formthe housing 56 of the bearing unit 30, cannot satisfactorily be bondedto a metal as the case may be. Since the housing 56 of the bearing unit30 is formed from a synthetic resin while the cylindrical portion 130 ofthe housing 121 is formed from a metal, they have to be fixed to eachother mechanically. In this embodiment, the synthetic resin-made housing56 of the bearing unit 30 is retained by riveting the to-be-rivetedportion 132 of the cylindrical portion 130 of the metal-made statorhousing 121. Namely, the synthetic resin-made housing 56 and metalliccylindrical portion 130 can mechanically be fixed to each otherpositively.

Next, a variant of the spindle motor 104 having the bearing unit 30installed in the stator housing 121 will be described with reference toFIGS. 26 and 27.

In this spindle motor 104, the bearing unit 30 is fixed to the statorhousing 121 by thermal riveting, not by riveting the cylindrical portion130.

In this variant, the bearing unit 30 fixed to the stator housing 121 hasa projection 141 formed on the bottom portion 62 of the housing 56 wherethe thrust bearing 66 is formed. The projection 141 is formed integrallywith the housing 56 formed from a synthetic resin. Namely, theprojection 141 is also formed from the synthetic resin. In this bearingunit 30, the projection 141 is inserted in a through-hole 142 formed inthe bottom of the cylindrical portion 130 and thermally deformed(riveted) at the free end thereof projected out of the through-hole 142.By thermally deforming the free end of the projection 141, the bearingunit 30 is secured to the stator housing 121.

FIG. 27 shows the bearing unit 30 in which there is provided only oneprojection 141 to secure the bearing unit 30 to the stator housing 121.It should be noted, however, that a plurality of projections 141 may beprovided as shown in FIG. 28. Also, in this bearing unit 30, theprojections 141 are inserted in through-holes 142, respectively, formedin the bottom of the stator housing 121, and thermally deformed at thefree ends thereof to secure the bearing unit 30 to the stator housing121.

Next, another variant of the spindle motor 104 having the bearing unit30 installed in the stator housing 121 will be described with referenceto FIGS. 29 and 30.

The bearing unit 30 fixed to the stator housing 121 of this spindlemotor 104 has an externally threaded projection 145 formed like theabove-mentioned projection on the bottom portion 62 of the housing 56thereof. On the other hand, the stator housing 121 has formed in thebottom of the cylindrical portion 130 thereof a screw hole 146 intowhich the threaded projection 145 is driven. By driving the threadedprojection 145 into the screw hole 146 with the bearing unit 30 beingreceived in the cylindrical portion 130, the bearing unit 30 isaccurately positioned and installed in place to the stator housing 121.

Note that the externally threaded projection 145 for fixing the bearingunit 30 to the stator housing 121 is formed as an projection, as shownin FIG. 30; but, it may be formed as an external thread 143 on the outersurface of the housing 56 at a portion near the bottom portion 62 asshown in FIG. 31. In this latter case, the screw hole formed at thestator housing 121 is formed as one equal in diameter to the housing 56.

According to the present invention, the spindle motor 104 may beconstructed as shown in FIG. 32. More specifically, in the spindle motor104, the bearing unit 30 has a metallic annular member 144 press-fittedon the outer surface of the synthetic resin-made housing 56 thereof.With the metallic annular member 144 and housing 56 being inserted inthe cylindrical portion 130 of the metallic stator housing 121, theouter surface of the metallic annular member 144 and inner surface ofthe metallic cylindrical portion 130 are bonded to each other with anadhesive. By installing the bearing unit 30 to the stator housing 121 inthis manner, the bearing unit 30 can be secured positively to thecylindrical portion 130 of the stator housing 121.

According to the present invention, the bearing unit 30 used in theaforementioned spindle motor 104 may be constructed as will be describedbelow with reference to FIGS. 33 to 36.

Each of the bearing units 30 shown in FIGS. 33 to 36 has a detent 147formed on the housing 56 thereof. The detent 147 of the bearing unit 30shown in FIG. 33 is a flat surface formed by flattening the lateral sideof the housing 56. The detents 147 of the bearing unit 30 shown in FIG.34 are a pair of opposite flat surfaces formed by flattening the lateralside of the housing 56. The detents 147 of the bearing unit 30 shown inFIG. 35 are a plurality of recesses formed in the outer surface of thehousing 56 to extend axially of the bearing unit 30 and along the heightof the housing 56 and each have a semicircular section. The detents 147of the bearing unit 30 shown in FIG. 36 are a plurality of ribs formedon the outer surface of the housing 56 to extend axially of the bearingunit 30 and along the height of the housing 56 and each have asemicircular section.

By forming the inner surface of the cylindrical portion 130 of thestator housing 121 correspondingly to the detent or detents 147 on theouter surface of the housing 56 shown in FIGS. 33 to 36, it is possibleto block the bearing unit 30 from being rotated when the bearing unit 30is introduced into the cylindrical portion 130 of the stator housing121.

Further, according to the present invention, the spindle motor 104 maybe constructed as shown in FIG. 37. The spindle motor 104 has a C-shapedmetallic retention member 148 formed at the top of the cylindricalportion 130 of the state housing 121, as shown in FIG. 37. The C-shapedmetal retention member 148 can be used to fix the housing 56 of thebearing unit 30 against axially coming out of the cylindrical portion130 of the stator housing 121.

Moreover, according to the present invention, the spindle motor 104 maybe constructed as shown in FIG. 38. The spindle motor 104 has the ironcore 123, having the excitation coil 122 wound thereon, installeddirectly to the outer surface of the housing 56 included in the bearingunit 30, as shown in FIG. 38. Thus, the cylindrical portion 130 includedin the aforementioned spindle motors 104 to install the excitation coil122 to the stator housing 121 is unnecessary, and thus the statorhousing 121 is constructed simpler, which will lead to a reducedmanufacturing cost. In this case, the housing 56 of the bearing unit 30may be fixed to the stator housing by either press-fitting or bonding.Alternately, the housing 56 of the bearing unit 30 may have anexternally threaded projection 149 formed on the bottom thereof, and thethreaded projection 149 may be driven into a screw hole 150 formed inthe stator housing 121 to fix the housing 56 to the stator housing 121.

Furthermore, according to the present invention, the spindle motor 104may be constructed as shown in FIG. 39. In this spindle motor 104, thehousing 56 of the bearing unit 30 and the stator housing 121 are formedintegrally with each other from a synthetic resin as shown in FIG. 39.Thus, the spindle motor 104 can be formed from a reduced number ofparts, which also will lead to a reduced manufacturing cost.

Also, according to the present invention, both the housing 56 of thebearing unit 30 and stator housing 121 may be formed integrally witheach other from a synthetic resin, as shown in FIG. 40. Alternately, anexternally threaded projection 151 of course can be formed integrally onthe bottom of the synthetic resin-made housing 56, as shown in FIG. 41.

By forming the housing 56 of the bearing unit 30 and the stator housing121 integrally with each other from a synthetic resin as above, it ispossible to reduce the necessary number of parts of the spindle motor104, make the assembling process for each part unnecessary andmanufacture the spindle motor more easily.

The bearing unit used in the aforementioned spindle motor supports therotating shaft rotatably in relation to the housing. According to thepresent invention, however, the housing may be adapted to be rotatablein relation to the shaft of the bearing unit.

An example of the spindle motor using a bearing unit whose shaft isfixed will be illustrated and explained hereinbelow.

Note that in the following illustration and explanation, the same orsimilar elements of these bearing unit and spindle motor as those of thebearing units 30 and the spindle motors 104 using the bearing unit 30will be indicated with the same or similar references as those used inthe illustration and explanation of the bearing units 30 and spindlemotors 104 and will not be explained in detail any longer.

The spindle motor in which the shaft of the bearing unit is fixed isgenerally indicated with a reference 204 in FIG. 42. As shown, in thespindle motor 204, the shaft 51 of the bearing 30 is fixed to the statorhousing 121. The shaft 51 is press-fitted at the fixing portion 52thereof projecting out of the housing 56 into a fixing hole 152 formedin the stator housing 121, and fixed to the stator housing 121. With theshaft 51 being thus fixed in the bearing unit 30, the housing 56 issupported rotatably in relation to the shaft 51.

The stator housing 121 having the shaft 51 fixed thereto has acylindrical coil fixture 153 formed to enclose the housing 56 of thebearing unit 30. Around the coil fixture 153, there is installed theiron core 123 having the excitation coil 122 wound thereon.

According to this variant, the spindle motor 204 has the rotor 115thereof installed to the housing 56 supported rotatably in relation tothe shaft 51. The rotor housing 120 has an engagement hole 14 formed inthe center thereof, and the bearing unit 30 has an engagement portion155 formed on the outer surface of the bottom portion 62 of the housing56 thereof. With the engagement portion 155 being press-fitted in theengagement hole 154, the rotor 115 is installed integrally with thehousing 56 to be rotatable.

Note that the engagement hole 154 is stepped at the inner surfacethereof and the engagement portion 155 is correspondingly stepped at theouter surface thereof to position the rotor 115 in relation to thehousing 56 to which the rotor 115 is to be fixed.

Also, in the spindle motor 204, the rotor magnet 119 is disposed on theinner surface of the cylindrical portion of the rotor housing 120oppositely to the excitation coil 122 on the stator 116. The rotorhousing 120 has formed on the outer surface thereof the turntable 117 onwhich the hard disc 103 is to be placed. The hard disc 103 also issupported at the inner circumference thereof between the turntable 117and chucking member 118 pressed toward the turntable 117 to be rotatablealong with the rotor housing 120.

According to the present invention, the bearing unit may be designedsuch that the shaft is rotatable or the housing is rotatable with theshaft being fixed. That is to say, either of such designs of the bearingunit according to the present invention may appropriately be selecteddepending upon how a motor or the like using the bearing unit isconstructed.

Note that in the bearing unit according to the present invention, if thehousing to support the metallic shaft is formed from a synthetic resinthat is electrically insulative, the static electricity charged on theshaft being rotated cannot be discharged surely to outside the bearingunit.

If such a bearing unit from which the static electricity charged on therotating shaft cannot be discharged to outside is used in a disc driveunit, there will arise the following problems.

Since there is not provided any discharge means or path from the shaftbeing a rotating part of the bearing unit, the hard disc installed onthe shaft will be charged with static electricity. For example, themagneto-resistive head to scan a hard disc and write or read informationsignals to or from it has a withstand voltage as low as 100 V or so, andthus will possibly be damaged by static electricity.

On this account, when the bearing unit according to the presentinvention is used in a disc drive unit or the like which writes or readsinformation signal to or from a disc therein and from which any smallinfluence of static electricity has to be removed, it should desirablybe constructed to discharge static electricity developed on the rotatingpart surely to outside.

Next, a bearing unit from which static electricity developed due to therotation of the shaft can be discharged to outside and a spindle motorusing the bearing unit will be described.

Note that in the following illustration and explanation, the same orsimilar elements of the bearing unit 30 and spindle motor 104 as thoseof the aforementioned bearing units and spindle motors will be indicatedwith the same or similar references as those used in the illustrationand explanation of the bearing units and spindle motors and will not bedescribed in detail any longer.

The spindle motor is generally indicated with a reference 104. Itemploys a bearing unit generally indicated with a reference 160 fromwhich static electricity developed due to the rotation of the rotatingshaft 51 can be discharged to outside the housing 56. The spindle motor104 is used in a disc drive unit like the spindle motor previouslydescribed with reference to FIG. 24.

The spindle motor 104 shown in FIG. 43 uses the bearing unit 160including a housing 156 formed from an electroconductive resin having aelectroconductive material mixed therein and which is constructed asshown in FIG. 44, which shows a fifth embodiment of the bearing unitaccording to the present invention. The electroconductive resin is apolycarbonate, polyester, nylon, polyimide, liquid crystal or the likein which conductive carbon or metal powder is mixed. Also, a syntheticresin having electroconductive carbon nanotube mixed therein so as to bemoldable with a high precision is used.

An electroconductive lubricant 157 is filled in the housing 156 formedfrom such an electroconductive resin. The lubricant 157 may be a machineoil such as esters, diesters, polyalphaolefin (PAO) or fluorinatedmachine oil in which an electroconductive material such as anelectroconductive carbon compound is mixed.

The radial bearing 55 received in the housing 156 is formed from theabove-mentioned electroconductive metal as sintered, brass or stainlesssteel.

Further, the rotating shaft 51 received in the housing 156 is formedfrom an electroconductive metal such as stainless steel.

The bearing unit 160 formed from the above-mentioned material has adischarge path from the rotating shaft 51 through the electroconductivelubricant 157 filled in the electroconductive housing 156 and radialbearing 55 to the housing 156 itself. That is, the bearing unit 160 candischarge static electricity developed when the rotating shaft 51rotates inside the housing 156 along the discharge path to outside thehousing 156.

In the spindle motor 104 using the bearing unit 160 having such adischarge path, static electricity developed due to the rotation of therotating shaft 51 can be discharged to the cylindrical portion 130formed integrally with the metallic stator housing 121 included in thestator 116, as shown in FIG. 43. Since in the spindle motor 104 usingthe bearing unit 160 according to the present invention, the staticelectricity developed when the rotating shaft 51 rotates can bedischarged to the stator housing 121, it is possible to prevent thestatic electricity from being charged to the hard disc 103 through theturntable 117. Thus, the magnetic head for writing or readinginformation signals can be protected against damage since it can beprevented from having the static electricity discharged thereto.

To define the discharge path from the rotating shaft of the bearing unitto the stator housing of the spindle motor, the bearing unit may beconstructed, as shown in FIG. 45, showing a variant of the fifthembodiment of the bearing unit. As shown, the bearing unit 160 includesa housing 166 formed from a synthetic resin which is electricallyinsulative, such as polyimide, polyamide, polyacetal or the like, andwhich has buried therein a metallic discharge member 167 extendingbetween the inner surface and outer surface of the housing 166. Themetallic discharge member 167 is formed toroidally, for example, andprovided integrally in the housing 166 when the latter is formed byout-sert molding. The metallic discharge member 167 is formed from anelectroconductive metal such as brass, stainless steel, or a sinteredmetal. The metal discharge member 167 is in contact with the outersurface of the radial bearing 55 in the housing 166.

In the spindle motor 104 using the bearing unit 160 constructed asabove, static electricity developed when the rotating shafts 51 rotatecan be discharged to the stator housing 121 as in the spindle motor 104shown in FIG. 43.

Using the bearing unit according to the present invention as in theforegoing, it is possible to positively protect parts included in a discdrive unit, such as the magnetic head and others, against beinginfluenced by the static electricity.

Further, since the bearing unit according to the present invention isconstructed to prevent the lubricant filled in the housing from leakingout, the magnetic head and hard disc inside a disc drive unit can beprevented from being defaced with the lubricant. Thus, a disc drive unitcan be constructed which can write or read information signals safelywith a positive protection of the magnetic head and hard disc.

In the aforementioned bearing unit, the thrust bearing supporting theshaft in the direction of thrusting is formed as a pivot bearing whichsupports the shaft at one end of the latter, which is formed circular ortapered. According to the present invention, however, the bearing unitis not limited to a one using the pivot bearing but may be a one inwhich the shaft is supported at the one end thereof which is a flatsurface, not circular or tapered.

A bearing unit using a thrust bearing which supports the one end of theshaft in the direction of thrusting on a flat surface will be describedbelow with reference to FIGS. 46 and 47.

Note that in the following explanation, the same or similar elements ofthis bearing unit as those of the aforementioned bearing units areindicated with the same or similar references as those used in theillustration and explanation of the bearing units and will not bedescribed in detail any longer.

This bearing unit is generally indicated with a reference 230. As shownin FIG. 46 showing the sixth embodiment of the bearing unit according tothe present invention, the bearing unit 230 has the rotating shaft 51whose one end portion is formed to have a large diameter (indicated at areference 231). This large-diameter portion is referred to as“projection” hereinbelow. The projection 231 is formed like a discintegrally with the rotating shaft 51. The projection 231 may bepreformed separately from the rotating shaft 51 and joined to the end ofthe rotating shaft 51 under pressure. In this case, each of the rotatingshaft 51 and projection 231 is formed from a metal.

On the other hand, at the bottom of the housing 56 receiving the radialbearing 55 which supports the rotating shaft 51 circumferentially, thereis provided a thrust bearing 232 which supports the projection 231formed at the one end of the rotating shaft 51. The thrust bearing 232is formed like a disc whose diameter is larger than that of theprojection 231 in order to close an opening 61 a formed in the bottom ofthe housing 61. When installed to the housing 61, the thrust bearing 232is made to abut a positioning step 233 formed on the bottom of thehousing 61. Thus, the thrust bearing 232 is positioned in place forinstallation to the housing 61.

The thrust bearing 232 used in this bearing unit 230 is formed from ametal such as stainless steel.

A bottom portion 235 is provided at the side of the housing body 61where the thrust bearing 232 is disposed. The bottom portion 235 isformed by molding a synthetic resin and joined by ultrasonic or thermalwelding to the housing body 61 formed from a synthetic resin. It shouldbe noted that the bottom portion 235 may be formed integrally with thehousing body 61 by resin molding, such as the out-sert molding. Joiningthe bottom portion 235 to the housing body 61 provides a housing 56sealed except for the shaft insertion hole 65. At this time, thedisc-shaped thrust bearing 232 is made to abut the positioning step 233and thus is supported on the bottom portion 235 for installation to thehousing body 61.

On the side of the thrust bearing 232 that is opposite to the projection231, there are formed dynamic pressure producing recess 236 as shown inFIG. 47. Namely, the thrust bearing 232 is a dynamic-pressure fluidbearing. At the side of the thrust bearing 232 opposite to theprojection 231, there is provided the dynamic pressure producing recess236 formed from a combination of pairs of recesses 236 a, each pairforming a V shape, and a coupling recess 236 b coupling the pairs ofV-shaped recesses 236 a with each other circumferentially of the thrustbearing 232. The dynamic pressure producing recess 236 is formed suchthat the V shape of each pair of recesses 236 a is directed at thebottom end thereof in a direction R3 in which the rotating shaft 51rotates.

When the rotating shaft 51 rotates, the lubricant 57 filled in thehousing 56 enters and circulates through the dynamic pressure producingrecess 236 formed in the thrust bearing 232 formed as a dynamic-pressurefluid bearing to produce a dynamic pressure between the outer surface ofthe rotating shaft 51 and inner surface of the radial bearing 55. Theprojection 231 provided at the one end of the rotating shaft 51 thuswill be supported on the thrust bearing 232. The dynamic pressure thusproduced will minimize the friction between the rotating shaft 51 andthrust bearing 232 to assure smooth rotation of the rotating shaft 51.Especially in this embodiment, since the rotating shaft 51, supported bythe radial bearing 55 and thrust bearing 232 formed each as adynamic-pressure fluid bearing, rotates in the presence of the lubricant57, sliding sound and vibration usually caused by sliding of therotating shaft on the bearings can be minimized. Thus, the bearing unit230 according to the present invention is extremely calm and stable.

Also, since the thrust bearing 232 is formed to have a larger diameterthan that of the projection 231 provided at the one end of the rotatingshaft 51, so the rotating shaft 51 can be supported very stably.

The bearing unit 230 shown in FIG. 46 is assembled by introducing therotating shaft 51 with the projection 231 into the housing body 61formed by the out-sert molding of the synthetic resin on the radialbearing 55, the thrust bearing 232 is disposed at the bottom of thehousing body 61, and then the bottom portion 235 is welded to thehousing body 61.

Further, the dynamic pressure producing recess may be formed in the endface of the radial bearing 55, opposite to the projection 231 of therotating shaft 51. With the dynamic pressure producing recess thusprovided, it is possible to minimize more positively the sliding soundusually caused by sliding of the rotating shaft on the bearings and thusprovide the bearing unit 230 which is extremely calm and stable.

This bearing unit 230 can be applied very advantageously to the spindlemotor of the disc drive unit shown in FIGS. 21 to 23. Since the bearingunit 230 is very calm, namely, since it is a lower-noise andless-vibration type, the disc drive unit using this bearing unit 230 canwrite or read information signals very stably.

Note that the bearing unit 230 shown in FIG. 46 also may be providedwith the function of discharging the static electricity developed whenthe rotating shaft 51 rotates to outside.

Moreover, the bearing unit 230 shown in FIG. 46 may be provided with afixing means, such as an engagement portion, for mechanical fixation ofthe housing 56 to a mating part of a motor, such as the spindle motor.

The aforementioned bearing units according to the present invention isconstructed such that the lubricant filled in the housing is preventedfrom leaking out by controlling the gap between the outer surface of therotating shaft and the inner surface of the shaft insertion hole formedin the housing and through which the rotating shaft is introduced.According to the present invention, however, the bearing unit may beconstructed as will be described below to prevent the lubricant as aviscous fluid filled in the housing from leaking out.

Namely, the bearing unit that will be described below can surely preventthe lubricant from leaking to outside the housing even if the pressurein the housing having the lubricant filled therein changes due to anenvironmental change such as a barometric pressure change, a temperaturechange or the like.

Note that the bearing unit according to the present invention is adoptedin the motor 12 of the radiator 10 shown in FIGS. 4 and 5, and so thesame or similar elements as those of the radiator 10 will be indicatedwith the same or similar references as those used in the illustrationand explanation of the radiator 10 and will not be described in detailany longer.

The bearing unit in consideration is provided with a vent path toprevent any change of the pressure in the housing, especially, toprevent the pressure in the housing from rising.

The bearing unit is generally indicated with a reference 190 andprovided with a vent path 200. As shown in FIGS. 48 and 49, showing theseventh embodiment of the bearing unit according to the presentinvention, the bearing unit 190 includes the radial bearing 55 andthrust bearing 66 to support the rotating shaft 51 to be rotatable, andhas the vent path 200 formed in a housing 220 thereof having thelubricant 57 filled therein.

The vent path 200 is provided to prevent the lubricant 57 from leakingout of the bearing unit 190 due to expansion of air inside the housing220 of the bearing unit 190 under a reduced pressure caused by analtitude change or the like. As shown in FIGS. 48 and 49, the vent path200 is provided in one or more places in the housing 220, for example.In the embodiment shown in FIG. 49, the vent path is provided in threeplaces at every predetermined angle on the outer surface of the housing220. The vent paths 200 can easily be formed at the same time as thehousing 220 is formed by out-sert molding integrally on the radialbearing 55 having already received the thrust bearing 66 therein. Thatis, since the vent paths 200 can easily be formed at the same time asthe housing 220 and thrust bearing 66 are molded from a synthetic resin,even if they are to be formed in a complicated shape, so forming of thevent paths 200 will not add to the manufacturing cost of the bearingunit 190.

The vent paths 200 thus provided permit air from inside the radialbearing 55 to purge as the rotating shaft 51 is introduced into theradial bearing 55 for seating therein.

Each of the vent paths 200 shown in FIGS. 48 and 49 includes a firstpath 201 and second path 202. The first path 201 is formed radially ofthe housing 220 from an internal space 203 near the thrust bearing 66.The first path 201 is open at the inner end thereof to the space 203where the thrust bearing 66 is formed to project from the bottom portion62 of the housing 220. The first path 201 is open at the outer endthereof to the second path 202. The second path 202 is formed parallelto the axis of the housing 220 and open to the outer surface of thehousing 220. Even the relatively complicated vent paths 200, becauseeach consists of the first and second paths 201 and 202, can easily beformed at the same time as the housing 220 and thrust bearing 66 areformed by molding a synthetic resin.

FIGS. 50 and 51 show together the eighth embodiment of the bearing unitaccording to the present invention. This bearing unit is generallyindicated with a reference 250. FIGS. 50 and 51 are a sectional view anda bottom view, respectively, of the bearing unit 250. The eighthembodiment is a variant of the bearing unit 230 shown in FIGS. 48 and49, having formed therein the vent paths 200 different in shape fromthose in the bearing unit 230. The function of the vent paths is thesame as in the bearing unit 230 in FIGS. 48 and 49.

Each of the vent paths 200 of the bearing unit 250 shown in FIGS. 50 and51 consists of the first path 201 formed in the lower end portion of thehousing 220, and the second path 202 formed in the outer surface of thehousing 220 as in the bearing unit 190 shown in FIGS. 48 and 49. Forexample, for forming the housing 190 in FIGS. 48 and 49 by out-sertmolding, at least two different-directional mold tools are required.However, the vent paths 200 can be formed in the bearing unit 250 shownin FIGS. 50 and 51 by a one-directional mold tool because the first path201 is formed in the lower end portion of the housing 220. Thus, themold tool can be simplified in structure.

More particularly, for making a horizontal hole, the mold tool has to beslid horizontally. Namely, the mold tool should of a sliding type. Inthe bearing unit 250 shown in FIGS. 50 and 51, however, since the firstpath 201 directed radially of the housing 220 is open at the bottom ofthe latter, the paths can be formed by a one-directional mold tool.Therefore, the bearing unit 250 can be produced by forming the housing220 and sliding bearing 66 integrally with each other, and thus themanufacturing costs be reduced.

Note that the bottom end portion 51 a of the rotating shaft 51,supported on the thrust bearing 66, is tapered (indicated at a reference200E) toward the thrust bearing 66, which facilitates the insertion ofthe rotating shaft 51 into the radial bearing 55.

The bearing unit 190 shown in FIGS. 48 and 49 is to be used in the motor12 of the radiator 10 as shown in FIG. 5. It is installed to the holder37 of the stator yoke 33.

The bearing unit 190 having the vent paths 200 formed therein may beformed as shown in FIGS. 52 and 53.

The bearing unit 190 shown in FIG. 52 has the vent paths 200 including,for example, three sets of a first path 201 and second path 202. Thefirst paths 201 are concavities formed in three equal circumferentialsections on one end face of the housing 220. The second paths 202 areformed axially of the housing 220 and in parallel with each other. Asshown, each of the first paths 201 connects to a corresponding one ofthe second paths 202.

The bearing unit 190 shown in FIG. 53 has the vent paths 200 including,for example, three sets of a first path 201 and second path 202. Thefirst paths 201 are concavities formed in three places circumferentiallyequidistant from each other on one end face of the housing 220. Thesecond paths 202 are through-holes formed in three places correspondingto the first paths in the housing 220, axially of the housing 220 and inparallel to each other. Each of the first paths 201 connects to acorresponding one of the second paths 202 and communicates with outsidethe housing 220.

Having the vent paths 200 formed in the housing 220, communicating withoutside of the housing 220, the bearing unit can positively prevent thelubricant from leaking to outside the housing 220, even when thepressure inside the housing 220 having the lubricant filled therein isvaried due to an environmental change such as a barometrical pressurechange or temperature change.

Note that the vent paths 200, especially the first paths 201, shoulddesirably be formed with such intervals between them that the surfacetension of the lubricant 57 can be used to prevent the lubricant 57 fromleaking when the bearing unit is in its normal condition.

The bearing unit uses a lubricant as a viscous fluid filled in thehousing. However, the lubricant may be any one of various kinds ofviscous fluid that have a specific viscosity and show a specific surfacetension.

The bearing unit according to the present invention cannot only be usedas a bearing of a motor of a radiator or of a spindle motor of a discdrive unit but also as a bearing of various types of motors.

Further, the bearing unit according to the present invention is usablein a motor as well as in a mechanism with a rotating shaft and amechanism supporting a member that is rotatable in relation to a shaft.

INDUSTRIAL APPLICABILITY

As having been described in the foregoing, the bearing unit according tothe present invention includes a housing in which bearings supporting ashaft are encased and also in which a viscous fluid is filled. Thehousing has such a sealed structure except for the shaft insertion holeformed therein for the shaft to be exposed to outside and so that theviscous fluid filled in the housing can be prevented from leaking tooutside the housing. So, this housing structure to positively protectsvarious devices using the bearing unit, such as an informationrecorder/player.

Since the housing of the bearing unit, sealed except for the shaftinsertion hole, can be formed as a one-piece structure by molding asynthetic resin, the bearing unit can be produced easily andinexpensively.

Provided with a means for fixing the housing to a mating object, thebearing unit according to the present invention can be positioned forfixation to the mating object and thus provides a high-precision bearingmechanism.

Further, the bearing unit according to the present invention caneliminate the influence of static electricity developed when the shaftor housing rotates. Therefore, the various devices using this bearingunit, such as an information recorder/player, can be protectedpositively against such static electricity.

1. A bearing unit comprising: a shaft; a radial bearing to support theshaft circumferentially; a thrust bearing to support the shaft at one ofthe thrusting-directional ends thereof; and a housing in which theradial and thrust bearings supporting the shaft are disposed and aviscous fluid is filled; the housing having a hermetic structure exceptfor a shaft insertion hole receiving the shaft therein and in whichthere is defined between the outer surface of the shaft and the innersurface of the shaft insertion hole a gap having a sufficient width toprevent the viscous fluid filled in the housing from leaking to outside,wherein the end portion of the housing where the thrust bearing isdisposed is formed from a synthetic resin and joined by welding to thehousing body also formed from the synthetic resin and in which theradial bearing is disposed, wherein the thrust bearing supports aprojecting portion formed at one end of the shaft and which is larger indiameter than the shaft body, and has formed in the surface thereofopposite to the projecting portion of the shaft dynamic pressureproducing recesses to produce a dynamic pressure by the viscous fluid.2. A bearing unit comprising: a shaft; a radial bearing to support theshaft circumferentially; a thrust bearing to support the shaft at one ofthe thrusting-directional ends thereof; and a housing in which theradial and thrust bearings supporting the shaft are disposed and aviscous fluid is filled; the housing having a hermetic structure exceptfor a shaft insertion hole receiving the shaft therein and in whichthere is defined between the outer surface of the shaft and the innersurface of the shaft insertion hole a gap having a sufficient width toprevent the viscous fluid filled in the housing from leaking to outsidethe housing, wherein the end portion of the housing where the thrustbearing is disposed is formed, by outsert molding, integrally on thehousing body in which the radial bearing is disposed, wherein there isprovided inside the housing a come-off preventive portion to prevent theshaft from coming off in the direction of thrusting through the shaftinsertion hole.